1. Field of the Invention:
In the manufacture of most paper grades, a desideratum is to provide a mechanism for adjusting the discharge of the fluent system or stock onto the forming wire for controlling profile.
The need for an adequate mechanism is dictated by the difficulties inherent in the building of a headbox capable of providing a so-called perfect jet across the machine width, i.e. a jet which discharges free of variations in terms of both quantity and speed across the machine. The width measurement, incidentally, grows with each successive generation of sophisticated papermaking machinery, widths of up to 400" now being commonplace.
The front wall beam of a headbox defines the component which carries the upper lip structure constituting the upper edge of the slice. Reformation of such a front wall beam or deflection thereof will influence the geometry of the lip slice and therefore the transverse profile or cross section of the stream of pulp stock flowing through the slice onto the wire.
2. Description of the Prior Art
Various earlier patents have been known to approach the broad problem from different angles.
U.S. Pat. Nos. 3,769,154 to Wolf, 3,976,539 to Kirjavainen, and 4,008,123 also to Kirjavainen, each relate to the matter of compensating for inherent deflections in the slice area, these deflections being resultant from the very weight or stiffness of the slice structure, or the operating pressure under which the headbox is operative.
In times past, manual profiling has been achieved by the mechanical deformation of the slice lip, that is the upper portion or roof of the discharge orifice, through the use of spaced jacks positioned on and between the slice lip and some suitably near stationary surface. Actuation of the jacks was sufficient to deform the slice lip.
As computerized profile controlling became known, different mechanisms were incorporated into the jacking system, as witness U.S. Pat. Nos. 4,406,740 to Brieu and 4,505,779 to Boissevain.
The computer controlled systems have brought with themselves a problem only partly remedied and not totally eliminated thereby. That problem relates to the influence which one adjustment mechanism tends to exert on adjacent mechanisms. That is to say, when one jack is adjusted or corrected, neighboring jacks are affected. A simple correction in one jack compounds itself in a correction or recorrection of perhaps two or three or four or more other jacks, the damaging results being obvious.